When to Use Riser vs. Plenum Cables

Knowing when to use riser cables vs. plenum cables is essential in cabling applications, as both of these options meet different guidelines and consist of varying materials. Utilizing cables that have the necessary ratings for your building helps you adhere to fire safety codes and safeguard building occupants and assets.

Learn more about the distinctions between plenum and riser cabling and when to use both in this article.

What Is a Riser?

A riser is a vertical space within a building that runs between multiple floors, such as an elevator shaft or any other vertical conduit. It could also be a series of rooms within a structure or a self-contained room on every floor, used for electrical and fire suppression equipment.

These areas enable vertical distribution of utilities like water lines and communications wiring. Risers are not part of a building’s heating, ventilation and air conditioning (HVAC) system, which means cables used for these applications do not need to have stringent fire ratings.

What Is Riser Cabling?

Riser cabling is a type of cable that meets the fire safety standards necessary for use inside a vertical riser and other non-plenum environments. Riser cables are suited for confined areas that will prevent the spread of toxic fumes from burning cables in the event of a fire. They are not suitable for plenum applications.

The lower fire safety requirements of riser cabling make it ideal for non-plenum environments where smoke toxicity and exposure pose less danger or fires are less possible. Riser cables adhere to the UL 1666 standard for identifying the flame propagation height for cables used in riser applications.

Despite their lower requirements, riser cables still possess fire safety properties, such as flame retardant jackets, that enable contractors to safely use them in commercial and residential building applications. Using solid conductors inside riser cables enables them to provide optimal signal strength, less resistance and enhanced strength when being pulled through walls.

What Is a Plenum?

A plenum is a space within a building used for airflow and air recirculation in an HVAC system, which may often be located between a structural and dropdown ceiling or underneath a raised floor. These areas usually house cabling equipment for phone and computer networks.

Because plenums circulate air throughout a building, they need cables with higher fire ratings to avoid distributing smoke and toxic fumes into the air if a fire occurs. Plenum spaces are capable of quickly spreading fire and smoke due to being rich in oxygen. Plenum cables offer additional properties that riser cables do not have to lessen this fire hazard.

What Is Plenum Cabling?

Plenum cable typically consists of a flame-retardant, low-smoke jacket that emits a lower amount of fumes and can self-extinguish. This jacket can be a fluorinated ethylene polymer (FEP), polytetrafluoroethylene (PTFE) or low-smoke polyvinyl chloride (PVC).

Plenum cables adhere to the National Fire Protection Association (NFPA) standard of NFPA 90A, which covers the installation, maintenance, operation and more of HVAC systems and their related equipment. This guideline helps contractors halt smoke migration and prevent hazards like fires and gases from entering forced air systems.

Plenum cabling is often used for buildings like hospitals and schools due to its enhanced safety features. These characteristics mean construction companies can help building occupants see a lower risk of harm in fire-related emergencies.

The Difference Between Plenum and Riser Cabling

Now that you know more about each cable type, you may still wonder which is best for your particular application. Here is a summarized view of the key differences between plenum vs. riser cables that can steer you toward a decision:

  • Fire rating: Plenum cables require higher fire ratings due to their use in HVAC systems, which have an increased possibility of encouraging a fire in their oxygen-rich environments. Riser cables are better to use in settings where preventing the spread of toxic gases and smoke is not as critical, due to their lower fire ratings.
  • Burn emissions: Although plenum cables can still burn if they catch fire, their low-smoke jackets ensure fewer emissions are released into the air and enable a slower burn.
  • Protective jacket: The protective jackets for both riser and plenum cables usually consist of PVC, although plenum types combine PVC compounds with other materials possessing a high fire resistance.
  • Location: Riser cabling can be placed between a building’s walls and in other non-plenum environments like elevator shafts. Plenum cabling is used for areas with high air circulation like air ducts and can be found in large public facilities like airports that require increased safety measures.
  • Versatility: Plenum cables have more versatility regarding where they can be used — you can install them in both plenums and risers. However, riser cables can only be employed in riser spaces. They can never replace plenum cabling.
  • Cost: Plenum non-fiber cables tend to be more costly than riser cables due to the additional materials needed to make the cabling plenum-rated. That said, plenum fiber optic cables may be closer in price to riser cables, as these additional materials aren’t needed.

Common Acronyms for Plenum and Riser Cables

When searching for plenum or riser cables, you’ll likely see numerous acronyms describing both types. To familiarize yourself with these labels and ensure you get exactly what you’re looking for, explore their meanings below:

  • CMR: This acronym stands for communications riser, which encompasses cables that can be used in riser applications.
  • CMP: Communications plenum includes cables that can work for any plenum or riser space.
  • NFPA: The National Fire Protection Association creates the standards that cables must meet to be employed in residential and commercial applications for appropriate fire safety.
  • NEC: The National Electrical Code is a guideline under the NFPA that ensures electrical system safety to protect against electrical hazards.
  • CL2P and CL3P: Class 2 and Class 3 plenum cables are used for in-wall installation in plenum and riser spaces. The NEC classifies the difference between the two classes as Class 2 being intrinsically safe and a Class 3 circuit needing a protection device within the power supply to be intrinsically safe.
  • CL2R and CL3R: Class 2 and Class 3 riser cables are used for in-wall installation in riser spaces.

Contact AerosUSA Today for Cable Protection

If you need electrical cable protection products for your plenum and riser applications, get in touch with AerosUSA to enjoy durable and flexible solutions with quick turnaround times. Our customer-designed offerings and high-quality customer service ensure you get what’s required to finish your jobs and meet industry standards, whether you’re in engineering, renewable energy or another industry.

Explore our AETF solutions to get plenum-suitable sleeving for your cables. Contact us today to speak with us about a quote or get more information on our cable protection products.

Reviewed for accuracy by: George Sims.
George Sims is an engineering and service-oriented leader in Cable Protection and Cable Management Products. Focus is on 100% commitment to customer satisfaction. AerosUSA is a small, agile, independent company whose focus is on our customers.